A B S T R A C TThis paper presents an overview of the results of experimental and analytical studies of the seismic response of stiff and flexible retaining structures. These studies were motivated by very large dynamic forces in areas of high seismicity predicted by current seismic design methodologies based on the work of Okabe [3] and Mononobe and Matsuo [4]. However, there is no evidence of systematic failures of retaining structures in major earthquakes even when the ground accelerations clearly exceeded the design assumptions. The experimental program consisted of a series of geotechnical centrifuge model studies with different types of structures with cohesionless and cohesive backfill. Overall, the results of these studies show that the Mononobe-Okabe (M-O) method of analysis provides a reasonable upper bound for the response of stiff retaining structures and that flexible retaining structures experience loads significantly smaller than those predicted by this method. Moreover, for deep embedded structures the dynamic forces do not continue to increase with depth and gradually become a small fraction of the overall load on the walls.
Experimental and numerical studies of the seismic response of a deep, stiff basement structure were motivated by the fact that the current seismic design methodologies based on the work of Wood (1973) and Ostadan (2005) predict very large dynamic forces in areas of high seismicity. The experimental program consisted of a geotechnical centrifuge model with a basement structure embedded in cohesionless backfill. The numerical analyses sought to replicate the results of the centrifuge experiment and to validate the use of numerical analyses for the prediction of expected behavior. Overall, the results of this study show that the Mononobe-Okabe method of analysis provides a reasonable estimate of the expected response of stiff basement structures provided depth-averaged design accelerations are considered.
IntroductionThe introduction of more stringent seismic design provisions in recent updates of design codes, e.g. IBC 2012 and FEMA 750, has increased the demand on seismic design of retaining walls and basement structures and, hence, there is a need for appropriate analysis and design methodology. While not all codes are prescriptive in specifying a particular methodology, the most commonly recommended analyses for non-yielding or "rigid" walls (e.g., embedded structures and basement walls) are based on an elastic solution developed by Wood (1973). More recently, Ostadan (2005) proposed a simplified method that has the Mononobe-Okabe (M-O) method, based on work by Okabe (1924) and Mononobe & Matsuo (1929), as a lower bound and the Wood (1973) solution as an upper bound, which can be as much as 2 to 2.5 times greater than the M-O method. The principal problem for a designer is that at high design accelerations, > 0.5 g, these methods predict very large dynamic forces for non-yielding walls, which appear unrealistic in view of actual experience in recent earthquakes.
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